Javascript：計算最小/最大/平均值

Question

我在Java站點的html站點中編寫了此代碼，但工作不正常。 大多數情況下，它似乎忽略了一些條目，只是隨機選擇最小/最大值。 另外，當我嘗試計算平均值時，即使變量在開始時聲明為0，我還是得到了一個字符串而不是一個數字。 例如，執行0 + 1 + 1 + 2 + 3 + 5 = 011235而不是12。這是代碼，在此先感謝。

**編輯：我在最后添加了學生平均代碼，但是它不起作用，它在頁面上甚至“學生” + [i]部分都沒有顯示任何結果。 另一方面，parseInt（）命令起作用了，並使一切正常工作了，謝謝:)

<script language = "javascript">
function myFunction() {
var course0 = [];
var course1 = [];
var course2 = [];

var minstugrade = 100;
var maxstugrade = 0;
var minstugradetext = "";
var maxstugradetext = "";

var stuavgarr = [];
var minstuavg = 100;
var maxstuavg = 0;
var minstuavgtext = "";
var maxstuavgtext = "";

var mincougrade = 100;
var maxcougrade = 0;
var mincougradetext = "";
var maxcougradetext = "";

var mincouavg = 100;
var maxcouavg = 0;
var mincouavgtext = "";
var maxcouavgtext = "";
var couavg = 0;

//add form items to array
var x = document.getElementById("course0");
var i;
    for (i = 0; i < x.length ;i++) {
        course0.push(parseInt(x.elements[i].value));
    }   
var x = document.getElementById("course1");
var i;
    for (i = 0; i < x.length ;i++) {
        course1.push(parseInt(x.elements[i].value));
    }
var x = document.getElementById("course2");
var i;
    for (i = 0; i < x.length ;i++) {
        course2.push(parseInt(x.elements[i].value));
    }

    //calculate course & student min/max
    for (i = 0; i < course0.length; i++) {
    if (course0[i] < mincougrade) {
    mincougrade = course0[i];
    mincougradetext = "course0";
    }
    if (course0[i] > maxcougrade) {
    maxcougrade = course0[i];
    maxcougradetext = "course0";
    }
    if (course0[i] < minstugrade) {
    minstugrade = course0[i];
    minstugradetext = "student" + [i];
    }
    if (course0[i] > maxstugrade) {
    maxstugrade = course0[i];
    maxstugradetext = "student" + [i];
    }
    }   

    for (i = 0; i < course1.length; i++) {
    if (course1[i] < mincougrade) {
    mincougrade = course1[i];
    mincougradetext = "course1";
    }
    if (course1[i] > maxcougrade) {
    maxcougrade = course1[i];
    maxcougradetext = "course1";
    }
    if (course1[i] < minstugrade) {
    minstugrade = course1[i];
    minstugradetext = "student" + [i];
    }
    if (course1[i] > maxstugrade) {
    maxstugrade = course1[i];
    maxstugradetext = "student" + [i];
    }
    }

    for (i = 0; i < course2.length; i++) {
    if (course2[i] < mincougrade) {
    mincougrade = course2[i];
    mincougradetext = "course2";
    }
    if (course2[i] > maxcougrade) {
    maxcougrade = course2[i];
    maxcougradetext = "course2";
    }
    if (course2[i] < minstugrade) {
    minstugrade = course2[i];
    minstugradetext = "student" + [i];
    }
    if (course2[i] > maxstugrade) {
    maxstugrade = course2[i];
    maxstugradetext = "student" + [i];
    }
    }       

    //calculate course average
    for (i = 0; i < course0.length; i++) {
    couavg += course0[i];
    }
    couavg = couavg / course0.length
    if (couavg < mincouavg) {
    mincouavg = couavg;
    mincouavgtext = "course0";
    }
    if (couavg > maxcouavg) {
    maxcouavg = couavg;
    maxcouavgtext = "course0";
    }

    couavg = 0;
    for (i = 0; i < course1.length; i++) {
    couavg += course1[i];
    }
    couavg = couavg / course1.length
    if (couavg < mincouavg) {
    mincouavg = couavg;
    mincouavgtext = "course1";
    }
    if (couavg > maxcouavg) {
    maxcouavg = couavg;
    maxcouavgtext = "course1";
    }

    couavg = 0;
    for (i = 0; i < course2.length; i++) {
    couavg += course2[i];
    }
    couavg = couavg / course2.length
    if (couavg < mincouavg) {
    mincouavg = couavg;
    mincouavgtext = "course2";
    }
    if (couavg > maxcouavg) {
    maxcouavg = couavg;
    maxcouavgtext = "course2";
    }

    //calculate student average
    for (i = 0; i < course0.length; i++) {
    stuavgarr[i] += course0[i];
    stuavgarr[i] += course1[i];
    stuavgarr[i] += course2[i];
    }

    for (i=0; i < stuavgarr.length; i++) {
    stuavgarr[i] = stuavgarr[i] / course0.length;
    if (stuavgarr[i] < minstuavg) {
    minstuavg = stuavgarr[i];
    minstuavgtext = "student" + [i];
    }
    if (stuavgarr[i] > maxstuavg) {
    maxstuavg = stuavgarr[i];
    maxstuavgtext = "student" + [i];
    }
    }


    document.getElementById("studmaxgrade").innerHTML = "Student that achieved the max grade is " + maxstugradetext
    document.getElementById("studmingrade").innerHTML = "Student that achieved the min grade is " + minstugradetext
    document.getElementById("studmaxavg").innerHTML = "Student that achieved the max average is " + maxstuavgtext
    document.getElementById("studminavg").innerHTML = "Student that achieved the min average is " + minstuavgtext
    document.getElementById("courmaxgrade").innerHTML = "The course in which the max grade is scored is " + maxcougradetext
    document.getElementById("courmingrade").innerHTML = "The course in which the min grade is scored is " + mincougradetext
    document.getElementById("courmaxavg").innerHTML = "The course in which the max average grade is scored is " + maxcouavgtext
    document.getElementById("courminavg").innerHTML = "The course in which the min average grade is scored is " + mincouavgtext

    }
</script>

Answer 1

輸入的值是一個字符串，因此a + b將被解釋為將一個字符串附加到另一個字符串。

如果確保第一個參數（在這種情況下為a）是整數，則a + b將導致兩個參數在數學上相加

console.log( '0' + 1 + 2 + 3 + 4 );             //* outputs 01234
console.log( parseInt( 0 ) + 1 + 2 + 3 + 4 );   //* outputs 10

JSFiddle

Answer 2

首先，您似乎對document.getElementById感到非常困惑

這根本無法解決javascript變量......

這實際上是“通過其ID獲取文檔元素”。 這是一個使用方法的例子...

<html>
<img id='my_new_selfie' src='me.jpg'>
....
....
<script>
alert (document.getElementById('my_new_selfie').src)
</script>

這將簡單地彈出一個警報，其中包含描述id為'my_new_selfie'的文檔對象的src的文本。

[me.txt]

將document.getElementById引入javascript的原因是為了節省開發人員學習DOM（文檔對象模型）的權限，以便訪問對象。 它允許您簡單地給您一個對象id並使用該id對其進行更改

在上面的示例中，我可以使用腳本或按鈕來更改圖像源，例如，可以使用頁面上另一個對象的onclick事件，例如按鈕...

onclick='document.getElementById('my_new_selfie').src='new_pic_of_me.JPG'

它不用於標識javascript中的變量